Hydrophobic surfaces can be used to improve the liquid repellence of a product and/or stain resistance of the product. Products with surfaces which resist absorbing liquids can have a number of commercially beneficial features. Such features can include liquid repellent materials and/or liquid resistant finishes, self-cleaning finishes and/or finishes that have a self cleaning effect and/or stain resistance finishes. The mechanisms associated with liquid repellency and liquid adhesion are in part related to the surface-energy acting between the liquid and the surface in contact with the liquid. When the free surface energy between the surface and liquid is low, there is generally a weak bond or adhesion between the liquid and surface. In such situations, the liquid has a greater tendency to run off the surface and/or be adsorbed at a slower rate by the surface. As such, on such surfaces liquids tend to runoff non-flat surfaces and/or bead on flatter surfaces.
Hydrophobic materials are commonly used to form hydrophobic surfaces. Such materials include waxes, fluorinated polymers, silicones, and the like. These materials are used in vehicle waxes and/or cleaners, tire cleaners, leather polishes and/or cleaners, floor polishes and/or cleaners, etc. For instance, silicones, siloxanes and various fluoro-acrylate polymers are the predominant materials used in fabric water proofing formulations and have been used for many years to protect fabrics from moisture penetration. These formulations are generally sprayed topically onto a fabric surface, and after air curing or drying, provide effective water repellency to rain, moisture, as well as protection against various soils and stains.
Another mechanism for forming hydrophobic surfaces is by altering the topology of the surface of a material. It has been found that elevations or depressions having certain heights and separated by certain distances can create hydrophobic surfaces. These types of surfaces can result in droplet formation of liquids. This principle is borrowed from nature and specifically from the lotus plant. It is known that small contact surfaces can reduce Van der Waals interaction, which is in part responsible for adhesion to flat surfaces with low surface energy. The leaves of the lotus plant have elevations made from a wax, and these elevations tend to lower the contact area with water. Several patent applications disclose the use of these artificially formed elevations on various types of surfaces such as US 2002/0150723; US 2003/0108716 and WO 00/58410, all of which are incorporated herein by reference.
The fabrication of synthetic superhydrophobic surfaces typically involves surface modification resulting in nanoscale surface roughness (i.e., nanoparticles, photolithography, mesoporous polymers, surface etching), sometimes in conjunction with chemical modification to reduce surface energy. (Li, X. M.; Reinhoudt, D.; Crego-Calama, M. Chem. Soc. Rev., 2007, 36, 1529-1529). These materials often require harsh synthetic conditions (e.g., etching and high temperature) (Fresnais, J.; Chapel, J. P.; Benyahia, L.; Poncin-Epaillard, F. J Adhes. Sci. Technol., 2009, 23, 447-467; Hikita, M.; Tanaka, K.; Nakamura, T.; Kajiyama, T.; Takahara, A. Langmuir, 2005, 21, 7299-7302), complex fabrication techniques (Yang, H. T.; Jiang, P. Langmuir, 2010, 26, 12598-12604; Bravo, J.; Zhai, L.; Wu, Z. Z.; Cohen, R. E.; Rubner, M. F. Langmuir, 2007, 23, 7293-7298), and are often limited by the substrate type and geometry that can be successfully coated. (Hikita et al. 2005; Yang & Jiang, 2010; Furstner, R.; Barthlott, W.; Neinhuis, C.; Walzel, P. Langmuir, 2005, 21, 956-961).
It is evident that there is an unmet need for alternative methods of preparing superhydrophobic surfaces.